LLtogr

I have made some modifications to the original source as I
was trying to get Channel Islands grid references working.
As a result CI and XD prefixed squares now work, and there
is an additional cigrtoll for WV and WA references, which
may or may not work as expected. -- Chris


Programs for conversion of latitude and longitude to national 
grids of Great Britain and Ireland, and vice versa

K.D. Bennett

Department of Plant Sciences
University of Cambridge

This package consists of four utility programs to make 
conversions from latitude and longitude to national grid co-
ordinates for Great Britain and Ireland. They are not finely 
polished programs, but working utilities that do a job. There is 
a limited amount of checking on the input, for example, but 
bizarre input may produce bizarre results.

The programs are:

lltogbgr            Converts latitude and longitude to
                    co-ordinates of the Great Britain grid

lltoirgr            Converts latitude and longitude to
                    co-ordinates of the Ireland grid

gbgrtoll            Converts co-ordinates of the Great
                    Briatin grid to latitude and longitude

irgrtoll            Converts co-ordinates of the Ireland
                    grid to latitude and longitude

Each program can be run with no options, in which case it will 
prompt for input.

Input grid values should be in the form "TL933937" (for Great 
Britain) and "C367821" (for Ireland): note that there are no 
spaces.

Input latitude and longitude values on the command line take the 
form "1 34 56 55 32 10", where the first three values are 
degrees, minutes and seconds for longitude, and the second three 
values are degrees, minutes and seconds for latitude. All six 
values must be present, but decimals are allowed, and values can 
be zero: "1 30 30 55 30 0" is equivalent to "1 30.5 0 55.5 0 0". 
For longitudes WEST of Greenwich, the degree value should be 
entered as negative.

If the lltoxxgr programs are run without options, they prompt for 
each of the six input values in turn.

Conversion from longitude and latitude is by exact calculation 
using formulae and constants from the publications of the 
Ordnance Surveys of the two areas (see below). The reverse 
calculation is by successive approximation (make a guess, see how 
close it is, make a better guess, etc), and thus takes a little 
longer.

Output has been tested against examples given by the Ordnance 
Surveys and against values from maps. I use these programs, and I 
have put some effort into checking their accuracy. But I cannot 
accept responsibility for any errors or problems caused by use of 
these programs.

If you use the programs and find them useful, please let me know. 
If you use them and find them in error, I would also be 
interested to know.

The programs are available by anonymous ftp to
ftp-palecol.plantsci.cam.ac.uk, in directory pub/ll-to-gr.
There is zipped package of the four MS-DOS executables, together 
with a copy of this README (ll-to-gr.zip), and a gzipped archive 
file (ll-to-gr.tar.gzip) of the source code, a makefile, and a 
copy of this README. The source code is ANSI C, with no frills, 
and should compile on any ANSI C compiler.


References

Ordnance Survey 1995. The ellipsoid and the Transverse Mercator 
Projection. Geodetic Information Paper No 1. Ordnance Survey, 
Southampton.

Ordnance Survey 1950. Constants, formulae and methods used in 
Transverse Mercator Projection. HMSO, London.

Ordnance Survey 1967. The history of the retriangulation of Great 
Britain 1935-1962. HMSO, London.

Ordnance Survey 1953. Tables for the Transverse Mercator 
Projection of Ireland. Ordnance Survey Office, Dublin.


Disclaimer

Copyright (C) 1994 by K.D. Bennett.  No portion of these programs 
may be reproduced for use by a commercial facility without 
express written consent of the author. This work is supported in 
part by the University of Cambridge. Neither the author, nor this 
institution, nor any of its employees, makes any warranty, 
express or implied, or assumes any legal liability or 
responsibility for the usefulness of any portion of this program.  
This copyright message and disclaimer must accompany any 
reproduced portion of this program.